The modern inkjet printer is able to place millions of tiny ink droplets precisely on paper, fabric, ceramic and other materials to create an image. Inkjet printing has many applications, a few of which include: food, beverage, and medical packaging and large format applications such as billboards and banners. Power operational amplifiers fulfill an important role in the design and powering of inkjet printers.
Piezoelectric techniques directed to inkjet printing typically employ a crystal that flexes when a voltage pulse is applied to a piezo-transducer, thereby forcing a droplet of ink out of the nozzle. When a voltage pulse is applied to piezoelectric material, it deforms, forcing a tiny droplet onto a surface that is to be printed. When the voltage returns to zero, the material is restored to its original shape, drawing ink into the reservoir and thus preparing it for the application of the next drop. This cycle repeats many times per second, typically each time the print head makes a pass across the printing area.
A representative printing head configuration may employ an amplifier to drive many nozzles. The amplifier may be connected to any number of ports of the nozzles at any one instant. At any instant, the printer head carrying all the nozzles is emitting anywhere from, more or less, 0 to 1024 ink droplets as governed by the printing program instructions. For inkjet printer applications, a trapezoidal waveform profile, among others, causes ink to flow from the ink magazine to the nozzle chamber to supply ink for the next droplet to be dispensed.
Amplifiers are employed in a wide variety of settings in modern electronics, only one of which is for use in driving the printer head of an inkjet printer. It is desirable for the design of a power amplifier to be compatible with any arbitrary wave shape that may be desired for a given application or printing solution. One power amplifier that can reproduce a trapezoidal waveform is a linear power amplifier, typically in a Class B or AB configuration. FIG. 1 shows a simplified block diagram of a basic linear power amplifier with its power sources and a capacitive load. FIG. 2 shows a simplified and exemplary output stage of a Class B power amplifier.
A potential drawback with the basic linear power amplifier approach, however, is relatively high power losses. FIG. 3 shows various aspects of waveforms involved with driving a capacitive load in accordance with the configuration of the Class B amplifier shown in FIG. 2. Generally, where a trapezoidal signal of frequency f with maximal voltage of Vmax and a piezoelectric load that can be modeled as a capacitor C, the power losses can be modeled as approximately:Plosses=CfVpositive_constantVmax 
In the above equation, Vpositive_constant is the positive voltage supply (Vpositive in FIG. 2) of the linear power amplifier. For ease of calculation, it can be assumed that the negative supply Vnegative_constant is zero, i.e. the load is discharged via T2 in FIG. 2 to the ground. The power losses during the rising edge 307 of “Output Voltage” 301 shown in FIG. 3 are generally due to the voltage drop on transistor T1 201 shown in FIG. 2, while the power losses during the falling edge 308 are generally due to the voltage drop on transistor T2 202 and generally due to the fact that the capacitor is discharged to the ground or to a certain negative voltage.